Built-in connectors in which metal terminals from leads of an electronic part, such as a diode and a relay, connect to metal terminals mounted to a housing are known. When connecting the metal terminals of the electronic part to the metal terminals in the housing, the terminals generally overlap and are then laser welded, with the metal terminals in the housing side arranged down and the metal terminals of the electronic part side arranged up. FIGS. 5A and 5B show a conventional laser welding structure for connecting metal terminals of the electronic part to metal terminals mounted to the housing by laser welding.
The laser welding structure shown in FIGS. 5A and 5B is provided with a lower metal terminal 103 on an upper surface 101c of an insulating housing 101 so as to run along the upper surface 101c thereof. As shown in FIGS. 5A and 5B, the upper metal terminal 102 is bonded onto the lower metal terminal 103 by laser welding, with the upper metal terminal 102 of the electronic part overlapped on the lower metal terminal 103. A bonded section of the lower metal terminal 103 and the upper metal terminal 102 is of an elongated shape extending in a longitudinal direction. The width W2 of the lower metal terminal 103 is wider than the width W1 of the upper metal terminal 102. Further, an irradiation diameter of a laser bean LB is defined as D. The irradiation diameter D is narrower than the width W2 of the lower metal terminal 103 and is wider than the width W1 of the upper metal terminal 102. As a result, the irradiation diameter D provides proper melting and bonding of the upper metal terminal 102 and the lower metal terminal 103.
According to the laser welding structure shown in FIGS. 5A and 5B, the structure provides proper melting and bonding of the upper metal terminal 102 and the lower metal terminal 103 while avoiding undesirable discoloration and deformation of the housing 101, due to heat generated at the time of melting and bonding. The lower metal terminal 103 is mounted on the upper surface 101c of the flat housing 1 so as to run along the upper surface 101c thereof and the periphery of the housing is free of the bonded section of the upper metal terminal 102 and the lower metal terminal 103.
However, a technique of mounting the lower metal terminal 103 on the upper surface 101c of the flat housing 1, so as to run along the upper surface 101c thereof, is generally regarded as being difficult to assemble, as it is difficult to position the lower metal terminal 103 on the upper surface 101c. For this reason, the technique is not often used in manufacturing an electrical connector. Furthermore, when many lower metal terminals 103 are arranged on the housing 101, there is a danger of a short-circuit, because of the absence of an insulator (or a housing) between the lower metal terminals 103 adjacent to each other. Thus, a widened pitch between the adjacent lower metal terminals 103 is necessary, therefore impeding miniaturization of the entire electronic part containing the built-in connector.
Accordingly, when manufacturing the electrical connecter, a structure has been adopted in which the lower metal terminal 103 and the upper metal terminal 102 are arranged in a groove 101a formed in the upper surface 101c of the housing 101. FIGS. 6A and 6B show another known laser welding structure where the metal terminal of the electronic part is connected to the metal terminal mounted to the housing by laser welding. In the laser welding structure, the lower metal terminal 103 is arranged in the groove 101a formed in the insulating housing 101. The groove 101a is of a shape of extending in a longitudinal direction so as to correspond to a shape of the lower metal terminal 103. When arranging the lower metal terminal 103 in the grove 101a, it has been prevalent in general techniques, such as press-fitting and insert molding. Then, the upper metal terminal 102 is bonded on the lower metal terminal 103 by laser welding, with the upper metal terminal 102 of the electronic parts overlapped on the lower metal terminal 103. Herein, as shown in FIGS. 6A and 6B, the upper metal terminal 102 and the lower metal terminal 103 are arranged in the groove 101a, in a state where the upper surface 101c of the surrounding housing 101 is positioned higher than the upper surface 102a of the upper metal terminal 102.
As shown in FIGS. 6A and 6BB, the width W2 of the lower metal terminal 103 is wider than the width W1 of the upper metal terminal 102. Moreover, the irradiation diameter of the laser beam LB is D, which is narrower than the width W2 of the lower metal terminal 103 and is wider than the width W1 of the upper metal terminal 102. Additionally, the width W3 of an opening of the groove 101a is the same as the width W2 of the lower metal terminal 103 and is wider than the irradiation diameter D of the laser beam LB.
According to the laser welding structure shown in FIGS. 6A and 6B, the structure facilitates mounting of the lower metal terminal 103 in the groove 101a by the techniques such as press-fitting and insert molding. Further, when many lower metal terminals 103 are arranged in the housing 101, the insulator interposed between the lower metal terminals 103 adjacent to each other eliminates a danger of short-circuit, thereby attaining a narrow pitch design. This favorably contributes to miniaturization of the entire electronic part with built-in connector.
FIG. 7 is a perspective view of another known laser welding structure, as disclosed in Japanese Published Unexamined Application No. 11-215652. The laser welding structure shown in FIG. 7 is for bonding by laser welding a bend allowance part 202a of a tab terminal 202 on a bus bar (or lower metal terminal) 201 to be received in an electrical junction box (not shown). When performing laser welding, thin-walled sections 202b-202d are formed at the bend allowance part 202a of the tab terminal 202 and the laser beam LB is irradiated on these thin-walled sections 202b-202d from an oblique direction.
The known laser welding structures shown in FIGS. 6A, 6B, and 7, however, include several shortcomings. In other words, referring to FIGS. 6A and 6B, when the laser beam LB is irradiated to welding the upper metal terminal 102 and the lower metal terminal 103, heat generated by irradiation of the laser beam LB can cause discoloration or deformation of both side walls in the groove 101a of the hosing 101. Specifically, as shown in FIGS. 6A and 6B, a region A and a region A′ facing corresponding portions at which the upper metal terminal 102 begins melting by irradiation of the laser beam LB may cause discoloration or deformation due to melting and bonding heat.
Where the bus bar 201 of FIG. 7 is arranged along the housing, it is free from a danger of discoloration or deformation due to heat generated by melting and bonding but it is liable to cause an increase in size of an apparatus. In some instances, where the bus bar 210 is arranged in the groove of the housing and surrounds therewithin the bus bar 201 and the tab terminal 202, the structure can cause discoloration or deformation due to heat generated by melting and bonding.